Aliphatic polycarbonate polyols derived from the copolymerization of carbon dioxide and epoxides such as those described in U.S. Pat. No. 8,247,520 have recently emerged as promising materials for use in thermoset applications. Applications include polyurethane foams (WO2012/071505), thermoplastic polyurethanes (WO2013/138161), adhesives (WO2013/158621), coatings (WO2012/071505), SPUR sealants (WO2013/163442), and composites (WO2012/040454).
CO2-based polyols provide valuable features in these applications. Depending on the specific application, incorporation of these polyols can provide enhanced strength, high hardness, good adhesion, and UV resistance. However, incorporating these new polyols into thermoset formulations can present certain challenges. Among these challenges are high viscosity, variable compatibility with other polyols, sensitivity to certain urethane catalysts, and limited stability to extended heating.
There has been substantial effort to address the thermal instability of high molecular weight aliphatic polycarbonates derived from copolymerization of CO2 and epoxides; however, all such methods addressing the issue depend on cross-linking or endcapping reactions. Such strategies cannot be applied to polyols for thermoset applications since the —OH end groups of such polyols are a required feature for use in these applications and end-capping or cross-linking removes or masks the terminal —OH groups of the polymer chains.
Similarly, the present inventors have disclosed aliphatic polycarbonate polyol compositions with various endgroup modifications. Such end-group modifications introduce new functionality such as vinyl groups (WO2013/022932), epoxides (WO2012/094619), silanes (WO2013/163442), isocyanates (WO2013/138161) and various polar groups (WO2012/154849). Some of these modifications happen to also decrease the tendency of the polyols to degrade to cyclic carbonate at elevated temperature, but these modified compositions are no longer polyols in the strict sense since chain ends are no longer —OH groups.
As such, there remains a need for aliphatic polycarbonate polyols with improved stability, but which retain —OH end group functionality desirable for urethane and related thermoset applications.